When the pinball industry began in the early Thirties the
main competition to the fledgling pinball machines were the three
reel slot machines, commonly referred to as "bell machines".
Slot machines were still legal in many areas of the country at
that time and were a major product of the coin machine industry.

Slot machine players deposited many coins in a relatively
short period of time as opposed to pinball in which a game of 5
or 10 balls - at a penny or nickel a game - lasted a minute or
two. The introduction of electricity (first from batteries and
then A.C.) into pinball during the 1934-1936 period made possible
a new concept in pinball design, the "multiple coin" pinball. In
this type of pingame the player could deposit more than one coin
(if desired) before starting the game to increase his chances of
winning. In addition, in most of these games, the number of
balls per game was decreased to one and these games were soon
referred to as "one-ball machines".